The invention concerns: a polishing machine for stone materials, having multiple grinding heads aligned on two oscillating and parallel beams with variable offset, that is, a machine for polishing slabs and strips of materials such as marble, granite and hard stone in which the polishing heads are positioned in such a way as to make best possible use of the available space.
Prior art comprises polishing machines with multiple polishing heads arranged in a single row on a beam oscillating transversely with respect to the direction of motion of the stone materials, transported on a conveyor. The polishing heads, equipped with abrasive scrapers (fixed or oscillating) or rollers, are made to oscillate transversely in order to obtain a working surface which is much wider than the heads themselves. The oscillating frequency is high compared to the speed of advancement of the underlying slabs or strips to enable the head to repeat the pass over the surfaced covered by the same head or the preceding head. Consequently the transverse speed of the beam on which the polishing heads are positioned needs to be high in order to pass over the entire width of the slab or strip being polished.
Furthermore, such a polishing machine needs to be very long in order to have a sufficient number of heads to achieve the desired degree of grinding and/or polishing. It is common for the successive heads to have abrasive elements with variable cutting and polishing characteristics to achieve a completely finished slab or strip at the end.
Prior art also comprises a polishing machine equipped with a shuttle with a set of two polishing heads which moves over the surface to be polished, suspended on a mobile frame: the said heads on the shuttle are positioned at an adjustable distance from one another, so that, with their transverse motion and the successive positioning of the mobile frame in a longitudinal direction, they cover the entire surface of the slab or strip to be polished, limiting the interference of the worked surfaces and extending the in a transverse direction the area covered by the two heads as a result of the adjustable distance between the two heads.
However, the working capacity of this last type of polishing machine is limited, in relation to the quantity slabs that need to be able to be produced. In fact, the successive positioning of the mobile frame effectively reduces the overall working speed of the polishing machine, moreover, the heads are positioned to perform the same polishing action over the whole surface of the slab, even with repeated passes, being subsequently adjusted to perform the final polishing of the same slab. This entails an extremely low productivity.
Such prior art may be subject to considerable improvement with a view to the possibility of making better use of available space and of obtaining a polishing machine with a high productivity.
From the foregoing emerges the need to resolve the technical problem of obtaining the maximum productivity from the polishing machine without occupying a large working area also in terms of length.
The invention resolves the said technical problem by adopting: a polishing machine for stone materials comprising a conveyor belt for the slabs or strips to be polished, a beam made to oscillate on at least two transverse, fixed supports above the said conveyor, at least one oscillating mechanism, a number of polishing heads, aligned on the said beam and oscillating with it, a device for detecting the shape and/or dimensions of the slabs or strips, positioned upstream of the working area, a process and control calculator for the polishing machine, characterised in that it has a second beam positioned parallel to the said first beam, also equipped with a number of polishing heads, transversely aligned with the polishing heads of the said first beam, and made to oscillate synchronously with it, by means of adjustable coupling devices, that enable the distance between the rows of polishing heads on the said first beam and second beam to be varied.
Adopting, in a further and preferred embodiment: a braking mechanism, kept in the locked position for the entire duration of the working phase, to ensure that the mechanical coupling between the two beams is blocked.
Adopting, in a further embodiment: the said adjustable coupling devices consisting of at least one pair of screw devices connected to each other and to the respective beams, even driven synchronously by a control transmission.
Adopting, in a further preferred embodiment: the said braking devices being activated by remote control.
Adopting, in a further embodiment: the said braking devices consisting of at least one hydraulically or pneumatically controlled actuator for each extremity of the beam.
Adopting, in a further embodiment: the said braking devices consisting of at least one electrically controlled actuator for each extremity of the beam.
Adopting, in a further preferred embodiment: the shuttle of the said first beam is equipped with guide rails for the second beam.
Adopting, in a further embodiment: the braking devices act directly on the said guide rails connecting the two beams.
Adopting, in a second embodiment: each beam translating and being adjustable with respect to an intermediate point of the shuttle for the transverse oscillation on the frames on which they are supported and blocked, by means of the said braking devices, so as to define a precise distance between the rows of polishing heads positioned on the said beams.
Adopting, in a third embodiment: both beams being able to translate directly on the said transverse frames on which they are supported; they are blocked with respect to each other by means of the said braking devices acting on elements connected to the respective beams, so as to define a precise distance between the rows of polishing heads positioned on the said beams.
The advantages obtained with the present invention are: the polishing machine has the polishing heads arranged in a more compact configuration, as the heads are positioned on two beams instead of just one; this configuration enables the overall length of the machine to be reduced in that two polishing heads work simultaneously on adjacent areas of the same slab or strip to be polished, with the same degree of finishing; the two adjacent polishing heads reduce the amplitude of oscillation required by approximately half compared that required for the single row of heads, thereby increasing productivity.